1. Field of the Invention
The present invention relates to an image determining apparatus and an image forming apparatus, and more particularly, it relates to an image determining apparatus automatically determining whether an original image is a color image or a monochrome image and an image forming apparatus comprising the image determining apparatus for forming an image with a colorant of a color or a black colorant.
2. Description of the Related Art
In a general image forming apparatus such as a color copying machine, a printing method varies with whether an original image is a color image or a monochrome image. In other words, a color image is printed with colorants of chromatic colors such as C (cyan), M (magenta) and Y (yellow), for example, while a monochrome image is printed with an achromatic black colorant.
If a user of such a color copying machine must sequentially input the types (color or monochrome) of original images and perform operations varying with the original images, however, extremely complicated operations are required. In general, therefore, a method of automatically determining the type of each original image (this operation is hereinafter referred to as ACS (auto color select)) for printing the original image in response to the result of determination is employed for the color copying machine.
Therefore, a copy of the original image can be readily formed without requiring the user to input the type (color or monochrome) of the original image or change the copy operation in response to the type of the original image.
However, the conventional image forming apparatus clearly determines only whether the original image is a color image or a monochrome image. Also as to a subtle image almost indistinguishable between a color image and a monochrome image, therefore, the conventional image forming apparatus disadvantageously determines as either a color image or a monochrome image.
If the image forming apparatus makes false determination in this case, it follows that the subtle image is printed by a false printing method based on the false determination. Therefore, the user must search for a printed image (in particular, a copy of a color image falsely printed with a black colorant is referred to as “miscopy”) based on false determination every copying for recopying the image if necessary. When copying originals including a number of color images and monochrome images, therefore, the user must take the trouble of finding out miscopies from a number of copied papers for reprinting the same with extremely complicated operations.
Particularly when performing reprinting, the user must reread the original images through operations further requiring time in addition to the time for detecting the miscopies.
Further, it follows that a monochrome image falsely determined as a color image is subjected to color printing not with a black colorant but with all colorants of C (cyan), M (magenta), Y (yellow) and K (black). This state cannot definitely be regarded as preferable in consideration of the speed and the cost required for image formation, the picture quality and the like.